Roll stabilization system for marine vessels



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Nov. 22, 1960 J. H. CHADWICK, JR., ETAL ROLL STABILIZATION SYSTEM FORMARINE VESSELS Filed Sept. l?, 1956 2 Sheets-SkaaiI 1 56 A LFmMF//v/J/VGLE I 5 l A .sY/vc//R047 q' 5f/$99925 gil/1111111114'Il/1111111111111? n I I --mullll INVENTORS Jos-PH fl. c//Ao w/c ,J/e.JEROME BENTKOWSKY ATTORNEY Nov. 22, 1960 J. H. cHADwlcK, JR., Erm.2,950,959

ROLL STABILZATION SYSTEM FOR MARINE VESSELS Filed Sept. 17, 1956 2Sheets-Sheet 2 nited States ROLL STABILIZATION SYSTEM FOR MARINE VESSELSFiled Sept. 17, 1956, Ser. No. 610,210

14 Claims. (Cl. 114-126) This invention relates to activated fin controlsystems for the roll stabilization of marine vessels. More particularly,it concerns an improved system of this nature wherein computed liftorders for ap fins are given variable magnitude limits which follow thevariations that occur in the maximum lift coefficients of the flap finsdue to disturbances of the stream line at such fins and due to changesin vessel speed.

The evolution of stabilizing fins has shown a tendency towards higherand higher maximum lift coefficients, high lift being very desirable formost efficient operation. This trend has reached a plateau in theso-called ilap lin, which uses a plain trailing-edge flap tiltablydriven in the direction of tilt of the main fin more than one times theamount of main fin tilt to augment the maximum lift coefficient of themain fin.

However, the magnitude of a flap fins maximum lift coefficient isaffected when the flap fin is subjected to angle of attack disturbances,while the maximum lift coefiicient of a conventional simple fin remainsconstant. The angle of attack disturbance or stream line disturbancereferred to will hereinafter be termed the false angle of attack and isthe true angle of attack of the ilap fin minus its hull-referenced angleof tilt. A false angle of attack is said to be in the loading sense whenit is such as to produce a greater lift than would be produced in itsabsence, and in the unloading sense when it is such as to produce alesser lift than would be produced in its absence. False angles in theloading sense reduce the maximum obtainable positive lift of a flap finand increase the maximum obtainable negative lift. Conversely, falseangles in the unloading sense increase the maximum obtainable positivelift of a flap tin and decrease the maximum obtainable negative lift.Therefore, if a lift order for a flap fm is to be limited specificallyto prevent the flap fin from entering into a hydrodynamic condition ofstall or a state of cavitation, it is desirable that the limit imposedon the lift order be made to follow the false angle induced variation inobtainable maximum lift, at least as long as the lift order is not suchas to call for a lift that would mechanically overload the flap n andits actuating mechanism. When varied in this manner, there is noappreciable sacrifice in the sys-tems stabilizing capacity as comparedto the considerable sacrifi-:e that would result if the lift limit werexed near the lowest expected value of maximum lift.

Besides being affected by changes in the false angle of attack, theobtainable maximum lift for a flap tin is affected by changes in thespeed of the vessel. That is to say, both the maximum positive lift andthe maximum negative litt increase as the square of the speed increases.

Accordingly, by the present invention, the positive and negative limitsimposed upon the lift order for each flap fin, specifically to preventstall or cavitation, are both increased with increasing speed. And' atthe same time, as changes of false angle of attack occur to increase theloading on the flap fin, a decreasing limit is imposed on atent ()fi v2,96%,959 Patented Nov. 22, 196i! computed positive lift orders, and anincreasing limit is imposed on computed negative lift orders. Andconversely, as changes of false angle of attack occur to decrease theloading on the fin, an increasing limit is imposed on computed positivelift orders and a decreasing limit is imposed on computed negative liftorders. Thus, insofar as speed is concerned, the positive and negativelift order limits are symmetrically controlled; while insofar as falseangle of attack is concerned, the limits are anti-symmetricallycontrolled.

The lift order limit controlled by speed and false angle of attack isspecifically to prevent stall or cavitation, and in this respect permitsthe computed lift orders to call for fin lifts or righting moments up toa given proportion of the maximum obtainable lift at any instant,preferably up to about of this maximum.

However, there may be times when the fin lifts permitted by theanti-stall limiter would overload the flap fins and their respectiveactuating mechanisms. Hence, the present system is preferably alsoprovided with an overload limiter interposed between the lift ordercomputer and the anti-stall limiter for imposing a fixed limit on thelift order which cooperates with the variable or controlled limit,whereby both overload and stall are prevented.

The principal object of the present invention is to provide an improvedactivated iin control system for the roll stabization of marine vessels.

Another object is the provision of a roll-stabilizing activated fincontrol system for marine vessels wherein computed lift orders foractivated flap fins are given variable magnitude limits for optimumutilization of the stabilization capacity of the system.

Anc-ther object is to provide a system according to the foregoingobjects wherein the variable magnitude limits follow the variations thatoccur in the maximum lift coefficients of the flap fins due to changesin the false angle of attack of each fin and changes in vessel speed.

Another object is the provision of a novel arrangement for symmetricallycontrolling the anti-stall limits of positive and negative lifts calledfor by an activated flap fin control system insofar as vessel speed isconcerned, and for anti-symmetrically controlling such limits insofar asthe false angles of attack at the fins are concerned.

With the foregoing and other objects in view, the present inventionincludes the novel combinations and elements described below andillustrated in the accompanying figures, wherein Fig. l is a graphhaving lift coefficient versus angle of tilt curves for a flap lin fordifferent false angles of attack at a given vessel speed;

Fig. 2 is a schematic diagram of a preferred embodiment of the presentinvention;

Fig. 3 is a wiring diagram of a suitable form of the anti-stall limiterincluded in Fig. 2;

Fig. 4 is a sectional view showing mounting details of a lift sensorwithin the drive shaft of one of the flap fins of the present system;and,

Fig. 5 is a sectional view of a suitable form of the lift sensordepicted in Fig. 4.

in Fig. l, curve 6 shows the variation that the lift coefiicient CL of aflap fin undergoes for a given vessel speed when the angle of tilt vc ofthe flap fin changes and when there is no false angle of attack u'. Thiswould be the characteristic obtained in a calm sea where there is noappreciable vertical movement of the water nor of the flapfin equippedvessel. When conditions change to produce a relative vertical movementbetween the sea and the vessel resulting in a false angle of attack inthe loading sense, -l-a, a lift coefficient curve 7 results. Comparingcuv'e7 with curve 6, it is seen that false angles of attack thatincrease the loading on a ap fin reduce the maximum positive liftcoecient of the fin and increase the maximum Vnegative lift coefficientthereof. When conditions change to produce a relative vertical movementbetween the sea and the vesselresulting in a false .angle of .attack inthe unloading sense, ,-oc', a lift coefficient curve 8 results.Comparing curve S with curve 6, it is seen that false angles of attack-that decrease the loading on a flap fin increase the maximum positivelift coei'cient of the fin and decrease the maximum negative liftcoefficient thereof.

`Referring now to the schematic diagram of Fig. 2, a signal generatinglinear accelerometer or roll pendulum 1.0 is mounted with its sensitiveaxis disposed athwartship, and provides a reversible phase alternatingcurrent signal whose magnitude is proportional to the roll angle of thevessel and Whose phase depends on the sense of the roll angle withrespect to the apparent vertical. The roll angle signal is impressedacross the winding of a poten# tiometer 11, the adjustable wipe-r ofwhich is connected to the input of a summing amplifier 12.

A signal generating rate gyro 13 is mounted on the vessel so as to besensitive to the roll rate of the vessel. The rate gyro providesatreversible phase alternating current signal whose magnitude isproportional to the roll 4 v tion 22 through a distance proportional tothe lift orde output signal of amplifier 12, so long as the lift calledfor does not exceed a limit xed by limit stop 21. This limit is toprevent overloading the stabilizing fins, and in this regard is fixedaccording to the maximum load desired upon the fins. It-is determined bythe spacing between a pair of rigid arms arranged to cooperate with atraveling nut on lead screw 20, t

When the lift called for by the output of amplifier 12 exceeds the limitfixed by limit stop 21, connection 22 is halted from being drivenfurther upon reaching a drive distance proportional to the limit. Slipclutch 19 prevents motor 18 from being overloaded in this event.

Since the rotor shaft of synchro generator 24 is driven by connection22, the output of synchro 24 is proportional to the computed lift orderup to the overload limit imposed on the order by limit stop 21. Thisoutput is fed i via a lead 5 to anV anti-stall limiter 26 which isprovided rate of the vessel and whose phase depends on the sense of therate. The roll rate signal is impressed across the Winding of apotentiometer 14, the adjustable wiper of which is connected to theinput of summing amplifier 12. This roll rate signal is the primarycontrol signal for the system, the signal provided by the linearaccelerometer having to do with long term roll displacements(stabilization to the apparent vertical rather than the true vertical)and the roll acceleration signal having to do with very short term rollmovements of the vessel. Thus, lit is primarily the roll rate signalwhich commands the righting moment to be produced by the fiapfin tocounteract the sensed roll rate, a predetermined relation existingbetween the direction of the sensed roll rate and the direction 0f therequired righting moment, e.g., the roll rate of one sense demands arighting moment of the opposite sense.

A signal generating angular accelerometer is mounted on Ythe vessel soas to be sensitive to the roll acceleration of vessel. The angularaccelerometer provides a reversible phase alternating currentvsignalwhose magnitude is proportional to the roll acceleration of the vesseland whose phase depends on the sense of the acceleration. The rollacceleration signal is impressed across the winding of a potentiometer16, the adjustable wiper of which is connected to the input of Ysummingamplifier 12.

The three signals separately generated through the effects of vesselmotion on the inertia-responsive signal generating devices 10, 13, 15are summed in amplifier 12 to provide an amplified output representingthe computed lift order which is to be limited according to the presentinvention. And in order that the control sensitivityV of the system maybe adjusted to conform with the requirements of various sea conditionsthat are encountered, a sea state selector or Weather adjustment isprovided. In the present embodiment, a knob 9 adjusts the magnitude ofthe sensor signals to the input of amplifier 12 by adjusting the wipersof potentiometers 11, 14, 16 simultaneously.

The lift order signal provided in the output of amplifier 12 is fed viaa lead 17 to a motor 18 whose output shaft is coupled through a slipclutch 19 to a lead screw 20 forming part of a mechanical limit stop 21.From lead screw 20, a mechanical connection 22 runs to the respectiverotor shafts of two variable transformer devices or synchro generators23, 24. Synchro 23 provides, on an output lead 25 thereof, adegenerative feedback signal to amplifier 12 which controls motor 18 todrive connecspecifically to prevent the lift order from calling for alift that would result in hydrodynamic stall or cavitation at theflap-fin. The limit imposed on the lift order signal by limiter 25 isvariably controlled in dependence upon an electrical input proportionalto the false angle of attack at one of the fins and in dependence upon amechanical input proportional to the square of the vessels speed.

Before proceeding with a detailed discussion of limiter 26,'it is deemedadvisable to enter upon a description of the elements arranged on theoutput side of limiter 26. Accordingly, the first of these elements isan amplifier 27 whose input receives the lift orderV output of limiter26 vi-a a lead 28. Amplifier 27 forms part of a servo loop forpositioning the stroke control lever 29 of a motordriven variabledelivery pump 30 which actuates a hydraulic ram 31 to tilt one of thestabilizing fins-specifically, a ap fin 32 rigged out substantiallyhorizontally near the turn of the bilge on the port side of the vessel.

The servo loop that includes amplifier 27 further includes a motor 33connected to the output of amplifier 27, anda pair of signal generators34, 35 mechanically cou-v pled to the drive shaft of motor 33. Signalgenerator 34 is of the tachometer type and provides a damping or speedfeedback signal to amplifier 27. t Signal generator 35 is of thevariable transformer or synchro generator type and provides a strokeposition feedback signal to amplifier 27. The coupling between the driveshaft of motor 33 and stroke synchro 35 includes irreversible gearing 36and a lever 37. Lever 37 operates the stroke control lever 29 ofvariable delivery pump 30. The output of the pump is applied to fintilting ram 31, which ram rotates fin 32 about its tilt axis 39 througha crank-40 on a rotatable stub shaft 41-to which the n is bolted. Forevery degree of rotation of fin 32, its flap is rotated through simplelinkage means (not shown) somewhat further in the same direction,preferably one and a half degrees.

It is desired to have ram 31 rotate fin 32 until water pressure on thefin produces an actual lift which is equal and opposite to that calledfor by the lift order signal on lead 28 to amplifier 27.V To accomplishthis, a signal proportional to actual lift is generated by a lifttransducer or `sensor 42 arranged within stub shaft 41 to sense theexceedingly slight but nevertheless measurable bending proportional tolift that occurs in ythe fins stub shaft. Figs. 4 and 5 respectivelyshow how the sensor maybe mounted and a suitable form of the sensor.These details Will be taken up hereinafter in the specificationf Thesignal proportional to actual lift obtainedfrom sensor 42 is fed to theinput of amplifier 27 via a lead 43. In amplier 27, the actual liftsignal is compared to the ordered lift signal received on lead 28. Theresult of this comparison is an output signal or error signal fromamplifier 27 proportionalrto the difference between the ordered lift andthe actual lift, respectivelyrepresented according to this error signal,whereby the tilt of ap 1in 32 is adjusted to obtain a lift at the iinthat reduces the error signal to zero.

Besides being fed to amplifier 27 of the stroke servo, the actual liftsignal is fed to the input of an amplifier 44 via a lead 4S tapped on tolead 43. Ampliiier 44 receives another signal in its input via a lead 46from one of the stator winding elements of a variable transformer deviceor synchro generator 47 whose rotor winding is angularly positionedaccording to the tilt of iiap iin 32 by a mechanical connection 4S toram 31 and energized according to the square of the vessels speed J by apair of electrical connections 49, t) across the wiper arm and one sideof a potentiometer 5l. The potentiometer itself is energized from asource of fixed AC. potential, and its output is caused to varyaccording to the square of speed, V2, by reason of its wiper beingdriven through a linkage 52 which is rotatably adjusted according to thesquare of the speed by the follower lever of a squaring cam 53 actuatedby a s eed adjustment knob 54. An indicator 55 coupled to knob 54 on theknob side of cam 53 is calibrated to show the speed for which linkage 52is adjusted.

Due to the energization of its rotor winding according to the square ofthe vessels speed, together with the angular displacement of its rotorwinding gccording to nn tilt, the signal produced by synchro generator47 on lead de is proportional to the product of the square of thevessels speed and the fins tilt angle, hence is proportional to the liftthat would be obtained in the absence of a false angle of attack at theiin.

The purpose of amplifier 44 is to provide a control signal for theanti-stall limiter 26 that is proportional to the vfalse angle of attackat tiap iin 32. Accordingly, amplilier 44 compares the actual liftsignal with the signal representing the lift that would be obtained withno false angle, and provides in its output a resultant signalproportional to the dierence between the iin angle measure and theactual lift or angle of attack measure and hence proportional to thefalse lift which in turn is proportional to the false angle of attack.

The false angle of attack signal from the output of amplifier 44 is fedvia a lead 56 to the anti-stall limiter 26. Referring now to the detailsshown in Fig. 3 of a suitable form of this limiter, it is seen that lead56 conneots to a tap 57. Moreover, one of the terminals of a source 58of fixed DC. potential, say the positive terminal, is connected to tapS7 through the winding of a potentiometer 59 in series with a fixedresistor 6ft. And the other or negative terminal of source 5S isconnected to tap 57 through the Winding of a like potentiometer 6i inseries with a like lixed resistor 62. The wiper arms of potentiometersS9, 6i are connected to each other through a ser-ies pair of oppositelypoled diodes 63, 64 and a lead 65 connects a tap 66 between the diodesto a junction terminal 67 for the limiters order -input lead 5, whichlead also includes a voltage dropping resistor 70, and for the limitersorder output lead 2S. The mechanical connection 52 (Fig. 2) rotates thewiper arms of potentiometers 59, 61 in opposite senses (as viewed inFig. 3) in an amount according to the square of the vessels speed. Thefrequency of the false angle signal output of amplifier 44 is the sameas the frequency of the order input on lead 5, by reason of the commonAC. power supply for the synchros 23, 24, and 47 and force transducer42, and the signals are either in phase or 180 out of phase, dependingon the angular relationship between the rotors of synchros 24 and 4' andthe direction of displacement of transducer armature 83 (Fig. 5) andhence, the phase is dependent upon the sense of the false angle ofattack and the sense of the input lift order.

Limiter 26, as depicted in Fig. 3, operates in a fullwave manner.Limiting of positive half cycles of the order input on lead 5 occurswhen the instantaneous magnitude of these positive half cycles, as theyappear at the anode of diode 63, exceeds the instantaneous magnitude ofthe net positive potential from source 58 and amplifier 44 at thecathode of diode 63, whereby diode 63 conducts and grounds the orderinput by way of the ground connection 68 on amplifier 44. Limiting ofnegative half cycles occurs when the instantaneous magnitude thereof atthe cathode of diode 64 exceeds the instantaneous magnitude of the netnegative potential from source 5S and amplifier 44 at the anode of diode64, whereby diode 64 conducts and grounds the order input by way ofground connection 63. A

if positive lift order signals on lead 5 are of a reference phase andnegative lift order signals are of opposite phase, then the false anglecontrol signals on lead 56 are of the reference phase for unloadingfalse angles and of the opposite phase for loading false angles.

Considering for ease of explanation only the positive half cycles of thelift order input signals on lead 5, the anti-symmetrical limiting oflimiter 26 insofar as its false angle control is concerned will nowbecome clear. When the lift order is positive and the false angle isunloading so that the respective signals therefor have the referencephase, the positive half cycles from amplifier 44 time coincident withthe positive half cycles on lead 5 add to the positive D.C. potentialpicked olf by the wiper of potentiometer 59 to produce a given limitinglevel for diode 63. Now if the lift order becomes negative while thefalse angle remains unloading, the negative half cycles from amplifier4.4 time coincident with the positive half cycles on lead 5 add to thepositive DC. potential picked o5 by the wiper of potentiometer S9 toproduce a limiting level for diode 63 that is less than the givenlimiting level. By similar analysis for loading false angles, it may bereadily shown that the limiting level for diode 63 is less for positivelift orders than for negative lift orders. Thus, it is seen how thelimits imposed by limiter 26 follow the false angle induced variationsin the maximum obtainable positive and negative lifts depicted in Fig.1.

The D.C. potential picked off by the wiper of potentiometer 59 is alwayspositive but is adjusted in magnitude according to the square of thevessels speed. As the vessels speed increases, the wiper ofpotentiometer 59 is manually adjusted by knob 54 (Fig. 2) toward thepositive side of D.C. source 58, thereby increasing tthe limitl' inglevel of diode 63 for both positive and negative lift orders. Similarly,the D.C. potential picked off by the wiper of potentiometer 61 is alwaysnegative but is adjusted in magnitude according to the square of thevessels speed. As the vessels speed increases, the wiper ofpotentiometer 6i is adjusted toward the negative side of D.C. source S,thereby increasing the limiting level of diode 64 for both positive andnegative lift orders. Thus, insofar as its control according to thesquare of the vessels speed is concerned, limiter 26 acts in asymmetrical fashion.

Referring now to the mounting details depicted in Fig. 4 for the liftsensor 42, the flap lin 32 is bolted to the stub shaft 41 which ishollow in configuration. Shaft 41 is journaled in spaced bearings 75, 76in a substantially cylindrical housing 77 for rotation about tilt axis39. Housing 77 in turn is provided with upper and lower stub shafts 78,79, respectively, for rotation about a substantially vertical axis S0for hn stowage purposes. The driving force for this vertical axisrotation is obtained from a pair of stowing ram connecting rods 8l, 82(see Fig. 2) linked to a cross-head plate 83 lixed to upper stub shaft7S.

Since flap iin 32 is rigidly bolted to stub shaft 41, this shaft issubjected to the entire stress produced by water action on the iin. Acircular plate 84 is rigidly secured around its rim, as by welding, tothe inner surface of shaft 4 1 and is positioned as near as convenientto the outboard end thereof. Rigidly bolted to this plate is acantilever beam 85 which extends substantially axially of shaft 41 V7toward the shafts inboard end. Rigidly and preferably vertically securedto shaft 41 adjacent the free` end of beam 85 and cooperable therewithis lift sensor 42 which Senses the deection of beam 85 due to the liftstress imparted to n support shaft 41, and provides a signalproportional to lift.

Any suitable type of lift sensor may be employed, and one form thereofis illustrated in Fig. 5. As shown, this sensor is an inductive pick-oidevice which comprises a threaded casing adjustably threaded in shaft 41and which has fixed thereto a pick-off core and winding S6 of theE-.transformer type. Two such cores may be provided for fail-safepurposes. A spring loaded plunger 87 having an armature 88 is operatedby movement of cantilever 85, andthe displacement of the armaturerelative to the core generates in the output winding of the pick-off asignal proportional to the lift stress or actual lift. This signal, asdescribed above, is compared with the ordered lift command output ofanti-stall limiter 26, and the iin tilting servo system reduces thediference therebetween to zero, thereby positioning the flap fin untilthe actual lift it imparts to the vessel is equal to the ordered lift aslimited.

`A mirror image 90 (Fig. 2) of tlap tin 32 is rigged out on thestarboard side of the vessel. A control arrangement 91 for starboard tin90 receives the ordered lift output of the overload limit stop 21 via aconnection 92 linked to connection 22. Control arrangement 91 includesidentical ones of all those components shown in Fig. 2 beginning with anorder synchro corresponding to order synchro 24. The signal phasing inarrangement 91, however, is such that the arrangement calls for apositive lift whenever the port iin arrangement calls for a negativelift, and vice-versa. Hence, the port and starboard ap ns 32, 90arecontrolled by similar yet independent means responsive to a commonsourceto assist each otherV in stabilizing the vessel in roll.V

While the invention is described in its preferred embodiments, it is tobe understood that the words used are words of description rather thanof limitation, and that changes within the purview of the appendedclaims may be made without departing from the true scope and spirit ofthe invention in its broader aspects.

What is claimed is:

1. In a control system for an activated iiap lin stabilizing surface ona marine vessel, the combination comprising, means responsive to therolling motion of said vessel for providing a lift order signalproportional to the lift required of said flap iin to counteract saidrolling motion, sensor means for providing a lift response signal inaccordancewith the Vactual lift produced by said flap fin, further meansresponsive to operation of said ilap iin for producing a limit controlsignal dependent upon variations occurring in the maximum liftcoeilicient of said ap fin due to disturbances of the lins angle ofattack relative to its angle of tilt with respect to said vessel, meansconnected to receive said lift order signal Yand controlled inaccordance with said limit control signal for varying the limits imposedon said lift order signal in accordance with said limit control signal,and means controlled in Vaccordance with the respective sginal outputsof said last-mentioned means and saidsensor means for adjusting saidangle of tilt of said flap iin to reduce the difference between saidrequired lift and said actual lift.

2. In a system for controlling the actuation of a ap lin stabilizingsurface tiltably mounted below the water line of a marine vessel andprojecting outwardly of said vessel on the beam thereof, the combinationcomprising, means responsive to the rolling motion of said vessel forproviding a lift order signal proportional to the lift required of saidflap iin to counteract said rolling motion, sensor means for providing aliftresponse signal `proportional to the actual lift produced by saidflap 'n, controllable limiter means coupled to said lift order signalproviding means for limiting said lift order signal, limiter controlmeans coupled with said limiter for controlling the limiting levelthereof according to the diterence between the angle of tilt of saidflap tin relative to the vessels hull and the angle of attack of said aplin, and means controlled in accordance with the respective signaloutputs of said limiter means and said sensor means for adjusting saidangle of tilt of said llap tin so that said flap fin produces an actuallift equal to the lift called for by the output of said limiter means.

3. In a marine vessel equipped with a tiltable flap fin stabilizingsurface for imparting righting moments to said vessel about the vesselsroll axis, the combination comprising, means responsive to the rollingmotion of said vessel for providing a signal according to the magnitudeand sense of the righting moment required of said ap iin to counteractsaid rolling motion, sensor means for providing a signal according tothe magnitude and sense of the righting moment actually produced by saidap iin, means connected to receive said sensor signal for providing acontrol signal according to the magnitude and loading sense of the falseangle of attack of said flap l'ln, controllable limiter means coupled tosaid control signal providing means and said required moment signalproviding means for limiting said required moment signal a lesser amountwhen it calls for an upward righting moment than when it calls for adownward righting moment providing that the false angle of attack is ofa sense to decrease the loading of said llap fin, and means coupled tothe respective outputs of said limiter means and said sensor means foradjusting the tilt of said ap iin to produce an actual righting momentequal to the righting moment called for by the signal output of saidlimiter means.

4. The system defined in claim 3 wherein the means for providing thefalse angle of attack signal includes means for generating a signaljointly proportional to the tilt of the flap iin and the square of thevessels speed, and means for comparing the last-mentioned signal withthe lift response signal provided by the sensor means.

5. In a marine vessel equipped with a tiltable ap n stabilizing surfacefor imparting righting moments to said vessel about the vessels rollaxis, the combination comprising, means responsive to the rolling motionof said vessel for providing a signal according to the magnitude andsense of the righting moment required of said ap fin to counteract saidrolling motion, sensor means for providing a signal according to themagnitude and sense of the righting moment actually produced by saidilap iin, means connected to receive said sensor signal for providing acontrol signal according to the magnitude and loading sense of the falseangle of attack of said flap n, controllable limiter means coupled tosaid control signal providing means and said required moment signalproviding means for limiting said required moment signal a greateramount when it calls for an upward righting moment than when it callsfor a downward righting moment providing that the false angle of attackis of a sense to increase the loading of said ap iin, and means coupledto the respective outputs of said limiter means and said sensor meansfor adjusting the tilt of said ap iin to produce an actual rightingmoment equal to the righting moment called for by the signal output ofsaid limiter means.

6. In a marine vessel equipped with a tiltable ap iin stabilizingsurface for imparting righting moments to said vessel about the vesselsroll axis, the combination comprising, means for providing a signalaccording to the roll rate of said vessel, said roll rate having apredetermined relation to the righting moment required of said ap iin tocounteract said roll rate, sensor means for providing a signal accordingto the righting kmoment actually produced by said flap fin, meansresponsive to said sensor signal for limiting said roll rate signal by avariable amount dependent upon variations occurring in the maximum liftcoefficient of said ap fin due to disturbances of the ap ins angle ofattack relative `to its angle of tilt with respect to said vessel,signal comparison means responsive to the respective outputs of saidsensor means and said limiting means for producing an error signalaccording to the dierence between the righting moment actually producedby said ap n and the required righting moment corresponding to the rollrate signal output of said limiting means, and drive means coupled tosaid comparison means for tilting said ap iin to reduce said errorsignal to zero.

7. In a marine vessel equipped with a tiltable iiap iin stabilizingsurface for imparting righting moments to said vessel about the vesselsroll axis, the combination comprising, means for providing a signalaccording to the magnitude and directional sense of the roll rate ofsaid vessel, said roll rate having a predetermined relation to therighting moment required of said flap iin to counteract said roll rate,sensor means for providing a signal according to the righting momentactually produced by said iiap iin, signal comparison means responsiveto the respective outputs of said sensor means and said roll rate signalproviding means for producing an error signal according to thedifference between the righting moment actually produced by said flaptin and the required righting moment corresponding to said roll ratesignal, controllable limiter means responsive to said roll rate signalfor preventing the roll rate signal supplied to said signal comparisonmeans from exceeding a preselected level which has the same magnitudefor roll rate signals of one directional sense as for roll rate signalsof the opposite directional sense, limiter controller means responsiveto said sensor signal for providing a measure of false angles of attackof a given loading sense at said ap iin and for increasing saidpreselected limit level for roll rate signals of said one directionalsense and decreasing said preselected limit level for roll rate signalsof said opposite directional sense by an amount proportional to saidfalse angles of attack, said lirniter controller means being responsiveto false angles of attack of a loading sense opposed to said givenloading sense for decreasing said preselected limit level for roll ratesignals of said one directional sense and increasing said preselectedlimit level for roll rate signals of said opposite directional sense byan amount proportional to said false angles of attack, whereby saidlimiter controller means anti-symmetrically controls the limiting levelof said limiter means, and drive means coupled to said signal comparisonmeans for tilting said liap nn in a sense to reduce said error signal tozero.

8. The combination claimed in claim 7 further including means forsymmetrically controlling the limiting level of the limiter means inaccordance with the square of the vessels speed.

9. In a system for controlling the actuation of a iiap tin stabilizingsurface tiltably mounted below the water line of a marine vessel andprojecting outwardly of said vessel on the beam thereof, the combinationcomprising, means responsive to the rolling motion of said vessel forproviding a reversible phase lift order signal oi magnitude dependentupon the amount of lit required o said flap iin to counteract saidrolling motion and of a phase dependent upon the sense of said requiredlift, sensor means responsive to the loading of said iiap fin forproviding a lift response signal according to the actual lift producedby said flap iin, means for providing a further signal dependent upon noperation, means responsive to said lift response signal and saidfurther signal for providing a reversible phase control signal havingthe same frequency as said lift order signal and having a magnitudedependent upon the amount of the false angie of attack of said iiap iinand a phase dependent upon the tin loading sense of said false angle ofattack, controllable limiter means coupled to said control signalproviding means and said lift order signal providing means for limitingsaid lift o-rder signal a greater amount for one phase thereof than forthe reverse phase thereof and vice-versa depending on the phase of saidcontrol signal, means coupled to the respective outputs of said limitermeans and said sensor means for providing an error signal according tothe difference between the ordered lift represented by the output ofsaid limiter means and the actual lift represented by the output of saidsensor means, and means responsive to said error signal for tilting saidiiap tin in a direction and amount to reduce said error signal to zero.

10. In `a control system for an activated ap iin roli stabilizingsurface on a marine vessel, the combination comprising, inertial meansresponsive to the rolling motion of said vessel for providing a liftorder signal having a magnitude and sense according to the lift requiredof said flap iin to counteract said rolling motion, sensor meansresponsive to the hydrodynamic loading imparted to said ap iin forproviding a lift response signal having a magnitude and sense accordingto the lift actually produced by said Hap iin, limiter means coupled tosaid inertial means for imposing anti-symmetrically varying stallprevention limits on opposite senses of said lift order signal, limitercontrol means responsive to said lift signal for controlling theanti-symmetrical variation of said limits about a preselected commonlevel thereof according to the magnitude and sense of said iin loading,signal comparison means coupled to the respective outputs of saidlimiter means and said sensor means for providing an error signalaccording te the difference between the ordered lift represented by thesignal output of said limiter means and the actual lift represented bythe signal output of said sensor means, and drive means coupled to theoutput of said comparison means for activating said flap tin to reducesaid error signal to zero.

ll. In `a roll stabilization system for marine vessels having anactivated iin for imparting righting moments to said vessel about itsroll axis and servomotor means for tilting said iin with respect to saidvessel, the combination comprising, means for supplying a iirst controlsignal in accordance with roll movements of said vessel, means forsupplying a second control signal in accordance with the li-ft impartedto the vessel by said iin, means for supplying a third control signal inaccordance with the Iangle of tilt of said iin relative to said vessel,variable limit means connected to receive said first control signal forlimiting the magnitude thereof, means responsive to said second andthird control signals and coupled with said limit means for varying thelimits imposed on said first control signal, and means responsive tosaid limited first control signal and said second control signal forsupplying a servomo-tor control signal.

l2. In a roll stabilization system for marine vessels having anactiv-ated flap iin for imparting righting moments to said vessel aboutits roll axis and servomotor means for tilting said iin with respect t-osaid vessel, the combination comprising, means for detecting andsupplying a measure of the roll movements of the vessel, means fordetecting and measuring both the angular displacement of the ilap iinwith respect to the vessel and the lift imparted to said vessel by saidap iin, means responsive to both said tin angle and fin lift measuresfor supplying a measure of the false angles of attack of said iin, meansfor providing a measure in accordance with the speed of the Vessel, andvariable limit means responsive to said false angles of attack measure,said speed measure, and said roll movement measure for limiting themagnitude of the roll movement measure within upper and lower limits inaccordance with changes in the value of the false angles of attackmeasure and said speed measure, said variable limit means being soconstructed and arranged that the upper and lower limits imposed on saidroll movement measure are anti-symmetrically varied in accordance withsaid false angles of attack and symmetrically varied in accordance withsaid speed measure.

13. Ina roll stabilization system for marine vessels having at least onen extending outwardly from the hull and adapted upon tilting thereof toproduce righting couples on the vessel and motive means for tilting saidiin, the magnitude of the maximum lift coefficient of said finincreasing with the magnitude of the angle of attack thereof, apparatusfor optimizing the lift capability Vof said iin under conditions ofvariation in the direction of the local flow streamlines at said n,comprising means for supplying a lift command signal, means forcontrolling said motive means in accordance with said corn mand signal,and means for modifying said command signal toprevent said iin fromexceeding an angle of attack corresponding to said maximum liftcoeiiicient, said modifying means including means for limiting bothpositive and negative excursions of said lift command'signal, means forproducing a signal representative of the cornponent of velocity of saidlocal ow streamlines mutually perpendicular to the tilt axis of said 1inand the longitu# dinal axis of the vessel, and means responsive to saidlast-mentioned signal for varying antisymmetrically the positive andnegative limits imposed by said limiting means upon s-aid lift commandsignal.

14. In a roll stabilization system for marine vessels having at leastone n extending outwardly from the 25 hull and adapted upon tiltingthereof to produce righting couples on the vessel and motive means fortilting said fin, the magnitude of the maximum lift coefficient of saidiin increasing with the magnitude of the angle of attack thereof,apparatus for optimizing the lift capability of said iin underconditions of variation in the direction of the local ow streamlines atsaid fin, comprising means for supplying a lift command signal, meansfor controlling said motive means in accordance with said commandsignal, means, for providing -a signal repre sentative of the componentof velocity of said local flow streamlines mutually perpendicular to thetilt axis of said fin and the longitudinal axis of the vessel, and meansfor modifying said lift command signal in accordance with the signal ofsaid last-mentioned means for preventing said iin from exceeding anangle of attack corresponding to said maximum lift coeicient.

References Cited in the file of this patent UNITED STATES PATENTS1,853,069 Minorsky Apr. 12, 1932 2,202,162 Minorsky May 28, 19402,234,326 Tiebel Mar. 11, 1941' 2,619,623 Meredith Nov. 25, 19522,701,111 Schuck Feb. 1,'1955 2,723,089 Schuck et al. Nov. 8, 19552,809,603 Bell Oct. 15, 1957 2,832,305 Bell Apr. 29, 1958

